This invention relates to laminated polymer films and, more particularly, to an opaque multilayer film inhibited against film-to-film blocking on one surface thereof, the opposite surface retaining a smooth, lustrous appearance and being especially well suited for such further film processing operations as metallization.
U.S. Pat. No. 4,377,616 describes a biaxially oriented opaque polypropylene film having excellent overall characteristics. To use this material for some commercial wrapping purposes, it is necessary that the film be further modified so as to permit printing thereon and to permit the heat sealing or adhesive sealing of the film to itself or other surfaces. In order to prepare the surfaces of polymeric films for ink receptivity or the adhesion of glues and adhesives, it is a common practice to treat the surface of the film to enhance the wettability of these materials. Common techniques employed to increase the wettability of such materials, e.g., polypropylene, include corona discharge treatment and flame treatment. In the case of the subject films, however, it has been found that such treatment leads to destructive film-to-film blocking.
By way of overcoming this destructive blocking tendency resulting from the foregoing surface treatment techniques, U.S. Pat. No. 4,560,614 provides an opaque film of the type described in U.S. Pat. No. 4,377,616 but in its surface treated form, containing finely divided talc in each of its skin layers to prevent film-to-film blocking. However, the presence of talc in both skin layers has been found to make these layers unsuitable for such further film processing operations as metallization.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a surface treated, non-blocking opaque polymer film possessing an anti-blocking agent-free surface of smooth and lustrous appearance which is suitable for such further film processing operations as metallization.
Broadly stated, the present invention provides a differential oriented polymer film comprising:
(a) a core layer containing numerous microscopic voids which impart an opaque, lustrous appearance to the exposed surface of the second skin layer of the film;
(b) a first skin layer of enhanced wettability on its exposed surface adhering to one surface of the core layer, said skin layer containing an anti-blocking effective amount of anti-blocking agent to render said layer substantially non-blocking; and,
(c) a second skin layer of enhanced wettability on its exposed surface adhering to the other surface of the core layer, said skin layer being substantially devoid of anti-blocking agent or any other component the presence of which would otherwise significantly attenuate the smooth and/or lustrous appearance of its exposed surface.
The term "differential" as applied to the oriented polymer film of this invention is intended to convey the distinctively dissimilar composition and appearance of each exposed film surface. Thus, whereas one exposed surface of the film is relatively rough and non-lustrous due to the incorporation of anti-blocking agent therein, and as such, is an unsuitable surface for some types of film processing techniques, metallization amongst them, the other exposed surface of the film, lacking as it does any anti-blocking component or other particulate ingredient, retains the opaque and lustrous appearance of the underlying core layer and as such is entirely suitable for other film processing procedures including metallization.